1. Field of Invention
The present invention relates to screens for displays of images and more particularly to screens used for the display and viewing of motion pictures including 3D cinema.
2. Discussion of Background
Screens for viewing cinema and other images are available in a wide range of structures and properties. The directivity of a screen relates to the amount or angle of specular reflection of light from the screen. In 2D cinema applications, the directivity of the viewing screen often has broad Gaussian like properties which reduce the apparent brightness of the screen (to an individual viewer), but maintain a very consistent relative image brightness across the screen at various angles such that image quality is consistent between the front, back, middle, and sides of the typical viewing audience.
In some 3D applications, such as polarization based systems, screens with high directivity are utilized because they have the capability of preserving polarization when light is reflected off the screen. Changes in polarization will typically cause crosstalk between the separately polarized left and right eye channels and thereby erode or even destroy the “3D” effect. However, such high directivity screens also produce undesirable effects such as hot spots and less uniform relative illumination across the screen. These problems can be exasperated at oblique viewing angles such that some viewing/seating positions in the theater may be less desirable or undesirable.
Spectral separation provides separation at the projector by filtering the left and right eye spectrally. The system differs from anaglyph in that the filters for the left and right eye each pass a portion of the red, green, and blue spectrum, providing for a full color image, and further differs from polarization based systems in that highly directive (or polarization preserving) screens are not needed, but can be utilized if the expense of greater hot spotting is deemed acceptable. The band pass spectrum of the left eye filter is complementary to the band pass spectrum of the right eye filter. The eyewear consists of filters with the same general spectral characteristics as are used in the projector.
All of the above methods for providing left/right eye separation for a 3D Stereoscopic presentation can be used with either two projectors (e.g., one for the left eye and one for the right eye), or may be used with a single D-Cinema projector system. In the dual projection system, the projection filter (e.g. spectral filter or polarization control) may be static or dynamic and may be located in front of the projection lens or inside the projector. In both 2D and 3D systems using dual projectors, the projectors are placed in close proximity to enhance alignment and uniformity of the projected images.